kravitz%network@ucsd.edu (Jody Kravitz) (02/06/90)
Recently I had a second, and then a third phone line installed. The original service was provided to my house by a five pair underground cable terminating on a four post carbon block protector. Only one pair was attatched. Activiating the second line required tieing down a second pair onto the unused posts of the protector block at the house, and also connecting that pair at the pole, about 600 feet from my house, to the appropriate cable pair. When the thrid line was installed, the simple protector block at my house was replaced with a modular box with "my side" which I can open and "their side" which can be opened only with a special tool. Their side has the underground cable termination, ground termination, and the protector blocks. My side has screw posts for each line and an RJ-11 connector for each line which I can unplug for testing. There is a "potted" circuit board underneath each RJ-11 jack. Our first line has always had a speakerphone (GTE model 08821) in the kitchen. The phone has an indicator light, "in use", which blinks when another phone on that line is off hook. Shortly after the installation of the third line, my wife noticed that the "in use" light on the speakerphone often blinked, even when I wasn't home. A quick check proved that neither the dog nor the two cats were making phone calls. I replaced the battery in the phone to no avail. I then measured the line voltage with a Fluke 77 DMM. The meter read 24 (+/- 0.1) volts. Everything I know about phones tells me it should be 48 volts. Measuring the second line gets wildly varying voltages, starting at about 40 volts when you first hang up, and fluctuating down to as low as 30 volts as time passes. Some questions: 1) Why is the open-circuit voltage on line 1 24 volts ? 2) Why does the second line's voltage vary so much ? 3) Can I fix my speakerphone to think 24 volts is on-hook ? 4) Would the readers be interested to have the schematic of the circuit board under the RJ-11 jack posted ? I derived this schematic by inspection: Line O-----------------------o---------o-----o | | | | | | | | (+) / | Cap |/ (o) (-) o-----o----|(trans) Res | | | |\ (o) (-) | | \ | Cap (-) (+) | | (+) Diode Diode | | | (+) (-) | o-----o | | | | | | | (o) o-----o-------o Res | (o) | | | | o--------o | o-----------------O To Phones | (+) Cap (-) | | (+) Diode (-) | (o) Res (o) | o-----------------O To Phones | o--------o | | | | | (o) o-----o-------o Res | | | (o) | | | | (+) (-) | o-----o Diode Diode | | | (-) (+) | | (+) | | / | Cap | | |/ (o) (-) o-----o----|(trans) Res | |\ (o) (-) \ | Cap | | (+) | | | | | | Line O-----------------------o---------o-----o I'm sorry, but I don't have any values to report for the components. I also do not know anything about the semiconductors. The installer claimed that from the central office they could use this circuit to determine: 1) Is there continuity on the line all the way to my house ? (A phone does not need to be connected for this test to work) 2) If there is a line-to-line short, which side of the circuit is the short on ? 3) If there is a line-to-ground short, which side of the circuit is the short on ? Does anyone know how this works or what prerequisite equipment must be in the CO ? Jody Kravitz P.S. To reply to me Internet: foxtail!kravitz@ucsd.edu uucp: ucsd!foxtail!kravitz